Nothing quite says "manly" like a cannonball with a handle. Fittingly, this intimidating weight, known as a kettlebell, comes with a testosterone-laden history: It debuted more than a century ago in Eastern Europe, where it was impressively hoisted by strongmen "in those full-body swimsuits and big mustaches," explains Patrick Castro, co-owner of the personal training studios BodySmith DC.

But somehow, as kettlebells have immigrated to the United States in the past few years (starting with the workouts of Special Forces guys and NFL players), the hefty spheres have attracted a new following: the ladies who lunge. "Women like to learn new things, while guys get macho and think they already know what they're doing," says Brian Wright, a local personal trainer.

So it's Wright's female clients who are often more receptive to discovering the benefits of kettlebell training, which isn't so much about lifting weight as it is about swinging it. The most basic move, in fact, is called the swing; it requires squatting to lift the handle with two hands, sticking out your rear end, thrusting your hips forward and using that momentum to send the kettlebell soaring up and back down into another swing. In just that one exercise, you've tested your strength (particularly in the hamstrings and glutes), your coordination and, with enough reps, your cardiovascular capacity.

Those combined challenges are what turns on Hope Hurt, a 26-year-old who was introduced to kettlebells when she began working with Wright a few months ago. "I started to prefer them over standard dumbbells," she says. "Dumbbells are old school. It's what my dad works out with." While he's doing the same boring sets and reps, Hope is perfecting her "Turkish get-up." Starting from a supine position with one arm reaching up holding a 20 - pound kettlebell, she contorts her body in a specific series so she ends up standing straight with the kettlebell above her head.

Exercises like this demand some serious muscle as well as core strength, but kettlebells' female following has discovered that the dynamic, full-body movements aren't designed to bulk you up. Rather, the result tends to be the long, lean look often associated with Pilates or yoga, Castro says.

Certainly, that perk was on the minds of the all-female crew hefting 10- to 25-pound kettlebells at a recent session of Castro's "Tactical Kettlebell Challenge" in his Glover Park studio. Kelley Auerbach, 43, a former bodybuilder, admitted she shies away from gaining too much mass but remains partial to the feeling of weightlifting, a feeling she can get with kettlebells. "I have trouble with cardio. With this, though, I don't feel like I'm doing the treadmill," she says.

Emily Field, 29, shows up at the class for the opposite reason. "I've always been more of a cardio person. I'm a hard sell for strength training," she says.

Both of them are getting the workout they crave, Castro says, because the movements require the raising of both weights and heart rates, which makes for an effective and engaging routine. "Women who don't have a lot of time and want the most bang for their buck? Frankly, that's kettlebells," he says.

Michelle Khai first laid eyes on kettlebells about six years ago while working at an Equinox Fitness Club in New York, and she found they jibed perfectly with her two passions: Olympic-style weightlifting and dance. With a kettlebell, she could perform effective lifts (like the snatch and the clean and jerk) more easily and do them in a flow that reminded her of her Alvin Ailey background.

So she wasn't surprised, as she started introducing the moves to clients, to discover that it was the female ones who usually picked them up faster. "Women are lower-body dominant, so we're used to powering up with our legs. And women tend to be more coordinated," Khai says. And when she took the bells to the Miami City Ballet to tone the dancers, the leotard set was also instantly smitten.

But Khai guessed a massive cannonball with a handle would need a makeover before it could take off with women who work out in their living rooms. So she created the "kbell," billed on her Kettlenetics Web site as "the most effective hand-held gym," a four-pound version with an attractive, cherry-red ball and a wide grip for comfortable handling. (She started marketing her bells via infomercials earlier this year.)

In this form, Khai hopes other women can understand the enormous potential of something that looks so simple. "Because of that handle, I can pass it around, flip it around," she says. "It opens up possibilities because you can kick with it, balance with it, flow with it. Part of my own practice I call my kettlebell flow. I turn on music and just play with it. It's an evolving movement art for me."

It also, she says, has done wonders for her tush. "We've coined the term 'bell butt' for that high, rounded look that every woman wants," says Khai, although the phrase would be just as appropriate for the soreness you're sure to feel in your seat a day or two after a kettlebell workout.

Or even right after. As she walked out of Castro's class in Glover Park, Kristi Bledsoe, 32, who had just touched kettlebells for the first time, declared, "My legs are about to give out." But would she be back? Definitely.